Encoder, decoder, encoding method, and decoding method

ABSTRACT

An encoder includes circuitry and memory coupled to the circuitry. The circuitry in operation: determines whether the shape of a current chroma block to be split satisfies a first condition; generates one or more second candidates for a block partitioning method by eliminating one or more predetermined candidates from a plurality of first candidates for a block partitioning method when the current chroma block satisfies the first condition; selects a block partitioning method from among the one or more second candidates; and splits the current chroma block according to the block partitioning method selected.

BACKGROUND 1. Technical Field

The present disclosure relates to an encoder that encodes a videoincluding a plurality of pictures, and related technologies.

2. Description of the Related Art

Conventionally, H.265 has been known as standards for encoding movingpictures. H.265 is also referred to as High-Efficiency Video Coding(HEVC) (H.265 (ISO/IEC 23008-2 HEVC)/HEVC (High Efficiency VideoCoding)) (see, for example, Non-patent Literature (NPL) 1).

SUMMARY

An encoder according to one aspect of the present disclosure includescircuitry and memory coupled to the circuitry. The circuitry inoperation: determines whether a shape of a current chroma block to besplit in an image satisfies a first condition; generates one or moresecond candidates for a block partitioning method by eliminating one ormore predetermined candidates from a plurality of first candidates for ablock partitioning method when the shape of the current chroma blocksatisfies the first condition; selects a block partitioning method fromamong the one or more second candidates; and splits the current chromablock according to the block partitioning method selected.

It should be noted that these generic or specific aspects may beimplemented using a system, a method, an integrated circuit, a computerprogram, or a non-transitory computer-readable recording medium such asa compact disc read only memory (CD-ROM), and may also be implemented byany combination of systems, methods, integrated circuits, computerprograms, and non-transitory computer-readable recording media.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1;

FIG. 2 illustrates one example of block splitting according toEmbodiment 1;

FIG. 3 is a chart indicating transform basis functions for eachtransform type;

FIG. 4A illustrates one example of a filter shape used in ALF;

FIG. 4B illustrates another example of a filter shape used in ALF;

FIG. 4C illustrates another example of a filter shape used in ALF;

FIG. 5A illustrates 67 intra prediction modes used in intra prediction;

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing;

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing;

FIG. 5D illustrates one example of FRUC;

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory;

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture;

FIG. 8 is for illustrating a model assuming uniform linear motion;

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks;

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode;

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing;

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing;

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1;

FIG. 11 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to a first aspect;

FIG. 12 is a diagram illustrating examples of a block partitioningmethod;

FIG. 13 is a diagram illustrating an example of a syntax tree indicatinginformation on a block partitioning method;

FIG. 14 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 1 of the first aspect;

FIG. 15 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 1 of the first aspect;

FIG. 16 is a flowchart illustrating a process of selecting a blockpartitioning method candidate when a current block to be split is ahorizontally elongated rectangle, according to concrete example 1 of thefirst aspect;

FIG. 17 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by the block splitterin the encoder according to the first aspect;

FIG. 18 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 2 of the first aspect;

FIG. 19 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 3 of the first aspect;

FIG. 20 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 3 of the first aspect;

FIG. 21 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 4 of the first aspect;

FIG. 22 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 4 of the first aspect;

FIG. 23 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 5 of the first aspect;

FIG. 24 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 5 of the first aspect;

FIG. 25 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to a second aspect;

FIG. 26 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 1 of the second aspect;

FIG. 27 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 2 of the second aspect;

FIG. 28 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 3 of the second aspect;

FIG. 29 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to the second aspect;

FIG. 30 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to concrete example 1 of the secondaspect;

FIG. 31 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to concrete example 2 of the secondaspect;

FIG. 32 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to concrete example 3 of the secondaspect;

FIG. 33 is a block diagram illustrating an example of implementation ofencoder 100;

FIG. 34 is a flowchart illustrating an example of an operation performedby encoder 100;

FIG. 35 is a block diagram illustrating an example of implementation ofdecoder 200;

FIG. 36 is a flowchart illustrating an example of an operation performedby decoder 200;

FIG. 37 illustrates an overall configuration of a content providingsystem for implementing a content distribution service;

FIG. 38 illustrates one example of an encoding structure in scalableencoding;

FIG. 39 illustrates one example of an encoding structure in scalableencoding;

FIG. 40 illustrates an example of a display screen of a web page;

FIG. 41 illustrates an example of a display screen of a web page;

FIG. 42 illustrates one example of a smartphone; and

FIG. 43 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[Underlying Knowledge Forming Basis of the Present Disclosure]

An encoder that encodes a video including a plurality of picturesincludes a block splitter that partitions each of the pictures intounits such as coding tree units (CTUs) and coding units (CUs) into whicha CTU is recursively split.

In the process of partitioning a picture into CTUs, the picture ispartitioned into CTUs, each having a fixed size, which areraster-scanned from upper left to lower right. The size of a CTU may beset to any pixel size among 16×16, 32×32, and 64×64, using any value of16, 32, and 64 which are multiples of 16.

In the process of partitioning a CTU into CUs, the CTU is partitionedinto CUs each having a variable size based on quadtree block splittingthat is recursive. A quadtree is a tree structure in which each board issplit into four branches. When a CTU is not to be partitioned, the CTUbecomes a CU and the size of the CTU becomes the largest size of a CU.The size of a CU may be set to any pixel size among 8×8, 16×16, 32×32,and 64×64.

In view of this, an encoder according to one aspect of the presentdisclosure includes circuitry and memory. Using the memory, thecircuitry: determines whether a shape of a current block to be split inan image satisfies a first condition; generates one or more secondcandidates for a block partitioning method by eliminating one or morepredetermined candidates from a plurality of first candidates for ablock partitioning method when the shape of the current block satisfiesthe first condition; selects a block partitioning method from among theone or more second candidates; and splits the current block according tothe block partitioning method selected.

This enables the encoder to generate, under a given condition, newcandidates for a block partitioning method by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod, and to split a current block into shapes corresponding to shapesobtained by using a block partitioning method selected from among thegenerated candidates. Accordingly, the encoder is capable, under a givencondition, of splitting the current block using the block partitioningmethod efficiently selected. In addition, the encoder is capable ofprohibiting the appearance of a block having a shape corresponding to ashape obtained by using a block partitioning method candidate that hasbeen eliminated. Therefore, when a coding mode is determined using anoptimization method such as a rate-distortion (R-D) optimization, thenumber of variations for carrying out trial calculations decreases andit is expected that the amount of processing for encoding decreaseswhile the degradation of coding efficiency is inhibited. Moreover, withthe encoder intentionally biasing the generation frequency ofinformation relating to a block partitioning direction, accuracy inprobability estimation in arithmetic coding using a context, such ascontext adaptive binary arithmetic coding (CABAC), increases, and theimprovement of coding performance can be expected.

The first condition is, for example, that the shape of the current blockis a rectangle.

With this, when the shape of a current block to be split is a rectangle,the encoder is capable of generating new candidates for a blockpartitioning method by eliminating one or more candidates from amultiple number of candidates for a block partitioning method, andsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from among the generatedcandidates. Accordingly, when the shape of the current block is arectangle, the encoder is capable of splitting the current block usingthe block partitioning method efficiently selected.

The first condition is, for example, that a ratio of a longer side to ashorter side of the current block is greater than a first value.

With this, when the shape of a current block to be split is a rectanglemore elongated than a predetermined shape, the encoder is capable ofsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from among candidates fora block partitioning method generated by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod. Accordingly, when the shape of the current block is a rectanglemore elongated than the predetermined shape, the encoder is capable ofsplitting the current block into the shapes corresponding to the shapesobtained by using the block partitioning method efficiently selected.

The first value is, for example, 2.

With this, when the shape of a current block to be split is a rectanglehaving the longer side that is two times as long as the shorter side,the encoder is capable of splitting the current block into shapescorresponding to shapes obtained by using a block partitioning methodselected from among candidates for a block partitioning method generatedby eliminating one or more candidates from a multiple candidates for ablock partitioning method. Accordingly, when the current block is arectangle having the longer side that is two times as long as theshorter side, the encoder is capable of splitting the current block intothe shapes corresponding to the shapes obtained by using the blockpartitioning method efficiently selected.

The first value is, for example, 4.

With this, when the shape of a current block to be split is a rectanglehaving the longer side that is four times as long as the shorter side,the encoder is capable of splitting the current block into shapescorresponding to shapes obtained by using a block partitioning methodselected from among candidates for a block partitioning method generatedby eliminating one or more candidates from a multiple number ofcandidates for a block partitioning method. Accordingly, when thecurrent block is a rectangle having the longer side that is four timesas long as the shorter side, the encoder is capable of splitting thecurrent block into the shapes corresponding to the shapes obtained byusing the block partitioning method efficiently selected.

The first condition is, for example, that the shape of the current blockis a rectangle and a length of a shorter side of the current block isless than a second value.

With this, when the shape of a current block to be split is a rectanglehaving the shorter side that is less than a predetermined value, thatis, when the current block has an elongated shape, the encoder iscapable of splitting the current block into shapes corresponding toshapes obtained by using a block partitioning method selected from amongcandidates for a block partitioning method generated by eliminating oneor more candidates from a multiple number of candidates for a blockpartitioning method. Accordingly, when the current block is a rectanglehaving the shorter side that is less than the predetermined value, thatis, when the current block has an elongated shape, the encoder iscapable of splitting the current block into the shapes corresponding tothe shapes obtained by using the block partitioning method efficientlyselected.

The second value is, for example, 64 pixels.

With this, when the shape of a current block to be split is a rectanglehaving the shorter side that is less than 64 pixels, the encoder iscapable of splitting the current block into shapes corresponding toshapes obtained by using a block partitioning method selected from amongcandidates for a block partitioning method generated by eliminating oneor more candidates from a multiple number of candidates for a blockpartitioning method. Accordingly, when the current block is a rectanglehaving the shorter side that is less than 64 pixels, the encoder iscapable of splitting the current block into the shapes corresponding tothe shapes obtained by using the block partitioning method efficientlyselected.

The first condition is, for example, that a ratio of a longer side to ashorter side of a block generated through the splitting of the currentblock is greater than a third value.

With this, when a current block is split into rectangles each being moreelongated than a predetermined shape, the encoder is capable ofsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from among candidates fora block partitioning method generated by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod. Accordingly, when the current block is split into rectangleseach being more elongated than the predetermined shape, the encoder iscapable of splitting the current block into the shapes corresponding tothe shapes obtained by using the block partitioning method efficientlyselected.

The third value is, for example, 4.

With this, when a current block is split into rectangles each having thelonger side that is four times as long as the shorter side, the encoderis capable of splitting the current block into shapes corresponding toshapes obtained by using a block partitioning method selected from amongcandidates for a block partitioning method generated by eliminating oneor more candidates from a multiple number of candidates for a blockpartitioning method. Accordingly, when the current block is split intorectangles each having the longer side that is four times as long as theshorter side, the encoder is capable of splitting the current block intothe shapes corresponding to the shapes obtained by using the blockpartitioning method efficiently selected.

The third value is, for example, 8.

With this, when a current block is split into rectangles each having thelonger side that is eight times as long as the shorter side, the encoderis capable of splitting the current block into shapes corresponding toshapes obtained by using a block partitioning method selected from amongcandidates for a block partitioning method generated by eliminating oneor more candidates from a multiple number of candidates for a blockpartitioning method. Accordingly, when the current block is split intorectangles each having the longer side that is eight times as long asthe shorter side, the encoder is capable of splitting the current blockinto the shapes corresponding to the shapes obtained by using the blockpartitioning method efficiently selected.

The one or more predetermined candidates include, for example, acandidate that splits a block having a shorter side and a longer side insuch a manner that a ratio of the longer side to the shorter sidefurther increases.

This enables the encoder to eliminate a block partitioning methodcandidate such that a current block is split into shapes each being moreelongated than before the splitting. The encoder is therefore capable ofprohibiting the appearance of an extremely elongated block that isexpected to hardly appear in the process of block partitioning.Accordingly, when a coding mode is determined using an optimizationmethod such as an R-D optimization, the number of variations for trialcalculations decreases and it is expected that the amount of processingfor encoding decreases while the degradation of coding efficiency isinhibited. Moreover, the encoder intentionally biases the generationfrequency of information relating to a block partitioning direction.Thus, accuracy in probability estimation in arithmetic coding using acontext, such as CABAC, increases, and the improvement of encodingperformance can be expected. The encoder is also capable of limiting theappearance of an extremely elongated block, and this in turn makes itpossible to improve subjective image quality.

The one or more predetermined candidates include, for example, acandidate that performs binary splitting on a block having a shorterside and a longer side in such a manner that a ratio of the longer sideto the shorter side further increases.

This enables the encoder to eliminate a block partitioning methodcandidate such that a current block is split into two blocks each beingmore elongated than before the splitting. The encoder is thereforecapable of prohibiting the appearance of an extremely elongated blockthat is predicted to hardly appear in the process of block partitioning.Accordingly, when a coding mode is determined using an optimizationmethod such as an R-D optimization, the number of variations for trialcalculations decreases and it is expected that the amount of processingfor encoding decreases while the degradation of coding efficiency isinhibited. Moreover, the encoder intentionally biases the generationfrequency of information relating to a block partitioning direction.Thus, accuracy in probability estimation in arithmetic coding using acontext, such as CABAC, increases, and the improvement of encodingperformance can be expected. The encoder is also capable of limiting theappearance of an extremely elongated block, and this in turn makes itpossible to improve subjective image quality.

The one or more predetermined candidates include, for example, acandidate that performs ternary splitting on a block having a shorterside and a longer side in such a manner that a ratio of the longer sideto the shorter side further increases.

This enables the encoder to eliminate a block partitioning methodcandidate such that a current block is split into three blocks eachbeing more elongated than before the splitting. The encoder is thereforecapable of prohibiting the appearance of an extremely elongated blockthat is predicted to hardly appear in the process of block partitioning.Accordingly, when a coding mode is determined using an optimizationmethod such as an R-D optimization, the number of variations for trialcalculations decreases and it is expected that the amount of processingfor encoding decreases while the degradation of coding efficiency isinhibited. Moreover, the encoder intentionally biases the generationfrequency of information relating to a block partitioning direction.Thus, accuracy in probability estimation in arithmetic coding using acontext, such as CABAC, increases, and the improvement of encodingperformance can be expected. The encoder is also capable of limiting theappearance of an extremely elongated block, and this in turn makes itpossible to improve subjective image quality.

For example, when the shape of the current block does not satisfy asecond condition, the circuitry encodes block partitioning informationrelating to the block partitioning method according to which the currentblock is split, and when the shape of the current block satisfies thesecond condition, the circuitry skips the encoding of the blockpartitioning information.

This enables the encoder to reduce an encoding load by skipping theprocess of encoding block partitioning information and writing abitstream into syntax as required by the encoding. Accordingly, theencoder is capable of improving coding efficiency.

The block partitioning information includes, for example, at least oneof a number into which the current block is split or a direction inwhich the current block is split.

This enables the encoder to include, into block partitioninginformation, information for uniquely determining a block partitionshape.

The second condition is, for example, that the block partitioning methodinvolves a partitioning direction and the shape of the current block isa rectangle.

This enables the encoder to skip the encoding of block partitioninginformation when the block partitioning method according to which acurrent block is split involves a direction and the shape of the currentblock is a rectangle. Accordingly, the encoder is capable of improvingcoding efficiency.

The second condition is, for example, that the block partitioning methodis binary splitting and the shape of the current block is a rectangle.

This enables the encoder to skip the encoding of block partitioninginformation when the block partitioning method according to which acurrent block is split is binary splitting and the shape of the currentblock is a rectangle. Accordingly, the encoder is capable of improvingcoding efficiency.

The second condition is, for example, that the block partitioning methodis binary splitting and a ratio of a longer side to a shorter side ofthe current block is greater than a predetermined value.

This enables the encoder to skip the encoding of block partitioninginformation when the block partitioning method according to which acurrent block is split is binary splitting and a ratio of the longerside to the shorter side of the current block is greater than apredetermined value. Accordingly, the encoder is capable of improvingcoding efficiency.

The second condition is, for example, that the block partitioning methodis ternary splitting and the shape of the current block is a rectangle.

This enables the encoder to skip the encoding of block partitioninginformation when the block partitioning method according to which acurrent block is split is ternary splitting and the shape of the currentblock is a rectangle. Accordingly, the encoder is capable of improvingcoding efficiency.

The second condition is, for example, that the block partitioning methodis ternary splitting and a ratio of a longer side to a shorter side ofthe current block is greater than a predetermined value.

This enables the encoder to skip the encoding of block partitioninginformation when the block partitioning method according to which acurrent block is split is ternary splitting and a ratio of the longerside to the shorter side of the current block is greater than apredetermined value. Accordingly, the encoder is capable of improvingcoding efficiency.

For example, the circuitry writes the first condition into syntax thatis a sequence layer, a picture layer, or a slice layer.

This enables the encoder to transmit, to a decoder, information relatingto a block partitioning method candidate to be eliminated. Accordingly,the decoder is capable of improving decoding efficiency.

For example, the circuitry writes the first condition into a sequenceparameter set (SPS).

This enables the encoder to transmit, to a decoder, information relatingto a block partitioning method candidate to be eliminated. Accordingly,the decoder is capable of improving decoding efficiency.

For example, a decoder according to one aspect of the present disclosureincludes circuitry and memory. Using the memory, the circuitry: parses,from an encoded bitstream generated by encoding an image, blockpartitioning information relating to a block partitioning methodaccording to which a current block to be split in the image is split;and splits the current block based on the block partitioning informationparsed. When a shape of the current block satisfies a first condition,the block partitioning information is generated by (i) generating one ormore second candidates for a block partitioning method by eliminatingone or more predetermined candidates from a plurality of firstcandidates for a block partitioning method and (ii) selecting a blockpartitioning method from among the one or more second candidates.

This enables the decoder to split a current block into shapescorresponding to shapes obtained by using a block partitioning methodselected from among candidates for a block partitioning method generatedunder a given condition by eliminating one or more candidates from amultiple number of candidates for a block partitioning method.Accordingly, the decoder is capable of splitting the current block intothe shapes corresponding to the shapes obtained by using the blockpartitioning method efficiently selected. In addition, the decoder iscapable, under a given condition, of prohibiting the appearance of ablock having a shape corresponding to a shape obtained by using a blockpartitioning method that has been eliminated. Therefore, when a decodingmode is determined using an optimization method such as an R-Doptimization, the number of variations for trial calculations decreasesand it is expected that the amount of processing for decoding decreaseswhile the degradation of decoding efficiency is inhibited. Moreover, thedecoder intentionally biases the generation frequency of the informationrelating to a block partitioning direction. This increases accuracy inprobability estimation in arithmetic decoding using a context, such asCABAD, and the improvement of decoding performance can be expected.

For example, when the shape of the current block does not satisfy asecond condition, the circuitry performs a decoding process by (i)parsing the block partitioning information relating to the blockpartitioning method according to which the current block is split and(ii) splitting the current block. When the shape of the current blocksatisfies the second condition, the circuitry performs a decodingprocess by splitting the current block without parsing the blockpartitioning information.

This enables the decoder to reduce the amount of decoding by notdecoding information relating to encoding and a bitstream generated bywriting block partitioning information into syntax. Accordingly, thedecoder is capable of improving decoding efficiency.

The block partitioning information relates to, for example, at least oneof a number into which the current block is split or a direction inwhich the current block is split.

This enables the decoder to include, into the block partitioninginformation, information for uniquely determining a block partitioningmethod.

The second condition is, for example, that the block partitioning methodis uniquely determined based on the shape of the current block.

With this, when a block partitioning method is uniquely determined basedon the shape of a current block to be split, the decoder is capable ofsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from among candidates fora block partitioning method generated by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod. Accordingly, when a block partitioning method is uniquelydetermined based on the shape of the current block, the decoder iscapable of splitting the current block into the shapes corresponding tothe shapes obtained by using the block partitioning method efficientlyselected.

The first condition is, for example, that the shape of the current blockis a rectangle.

With this, when the shape of the current block is a rectangle, thedecoder is capable of splitting the current block into shapescorresponding to shapes obtained by using a block partitioning methodselected from among candidates for a block partitioning method generatedby eliminating one or more candidates from a multiple number ofcandidates for a block partitioning method. Accordingly, when the shapeof the current block is a rectangle, the decoder is capable of splittingthe current block into the shapes corresponding to the shapes obtainedby using the block partitioning method efficiently selected.

The first condition is, for example, that a ratio of a longer side to ashorter side of the current block is greater than a first value.

With this, when the shape of the current block is more elongated than apredetermined shape, the decoder is capable of splitting the currentblock into shapes corresponding to shapes obtained by using a blockpartitioning method selected from among candidates for a blockpartitioning method generated by eliminating one or more candidates froma multiple number of candidates for a block partitioning method.Accordingly, when the shape of the current block is more elongated thanthe predetermined shape, the decoder is capable of splitting the currentblock into the shapes corresponding to the shapes obtained by using theblock partitioning method efficiently selected.

The first value is, for example, 2.

With this, when a current block is a rectangle having the longer sidethat is two times as long as the shorter side, the decoder is capable ofsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from candidates for ablock partitioning method generated by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod. Accordingly, when the current block is a rectangle having thelonger side that is two times as long as the shorter side, the decoderis capable of splitting the current block into the shapes correspondingto the shapes obtained by using the block partitioning methodefficiently selected.

The first value is, for example, 4.

With this, when a current block is split into rectangles each having thelonger side that is four times as long as the shorter side, the decoderis capable of splitting the current block into shapes corresponding toshapes obtained by using a block partitioning method selected from amongcandidates for a block partitioning method generated by eliminating oneor more candidates from a multiple number of candidates for a blockpartitioning method. Accordingly, when the current block is split intorectangles each having the longer side that is four times as long as theshorter side, the decoder is capable of splitting the current block intothe shapes corresponding to the shapes obtained by using the blockpartitioning method efficiently selected.

The first condition is, for example, that the shape of the current blockis a rectangle and a length of a shorter side of the current block isless than a second value.

With this, when a current block to be split is a rectangle having theshorter side that is less than a predetermined value, that is, when thecurrent block has an elongated shape, the decoder is capable ofsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from among candidates fora block partitioning method generated by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod. Accordingly, when the current block is a rectangle having theshorter side that is less than the predetermined value, that is, whenthe current block has an elongated shape, the decoder is capable ofsplitting the current block into the shapes corresponding to the shapesobtained by using the block partitioning method efficiently selected.

The second value is, for example, 64 pixels.

With this, when a current block to be split is a rectangle having theshorter side that is less than 64 pixels, the decoder is capable ofsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from among candidates fora block partitioning method generated by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod. Accordingly, when the current block is a rectangle having theshorter side that is less than 64 pixels, the decoder is capable ofsplitting the current block into the shapes corresponding to the shapesobtained by using the block partitioning method efficiently selected.

The first condition is, for example, that a ratio of a longer side to ashorter side of a block generated through the splitting of the currentblock is greater than a third value.

With this, when a current block is split into rectangles each being moreelongated than a predetermined shape, the decoder is capable ofsplitting the current block into shapes corresponding to shapes obtainedby using a block partitioning method selected from among candidates fora block partitioning method generated by eliminating one or morecandidates from a multiple number of candidates for a block partitioningmethod. Accordingly, when the current block is split into rectangleseach being more elongated than the predetermined shape, the decoder iscapable of splitting the current block into the shapes corresponding tothe shapes obtained by using the block partitioning method efficientlyselected.

The third value is, for example, 4.

With this, when a current block is split into rectangles each having thelonger side that is four times as long as the shorter side, the decoderis capable of splitting the current block into shapes corresponding toshapes obtained by using a block partitioning method selected from amongcandidates for a block partitioning method generated by eliminating oneor more candidates from a multiple number of candidates for a blockpartitioning method. Accordingly, when the current block is split intorectangles each having the longer side that is four times as long as theshorter side, the decoder is capable of splitting the current block intothe shapes corresponding to the shapes obtained by using the blockpartitioning method efficiently selected.

The third value is, for example, 8.

With this, when a current block is split into rectangles each having thelonger side that is eight times as long as the shorter side, the decoderis capable of splitting the current block into shapes corresponding toshapes obtained by using a block partitioning method selected from amongcandidates for a block partitioning method generated by eliminating oneor more candidates from a multiple number of candidates for a blockpartitioning method. Accordingly, when the current block is split intorectangles each having the longer side that is eight times as long asthe shorter side, the decoder is capable of splitting the current blockinto the shapes corresponding to the shapes obtained by using the blockpartitioning method efficiently selected.

The one or more predetermined candidates include, for example, acandidate that splits a block having a shorter side and a longer side insuch a manner that a ratio of the longer side to the shorter sidefurther increases.

This enables the decoder to eliminate a block partitioning methodcandidate such that a current block is further split into three blocksmore elongated than before the splitting. The decoder is thereforecapable of prohibiting the appearance of an extremely elongated blockthat is hardly predicted to appear in the process of block partitioning.Accordingly, when a decoding mode is determined using an optimizationmethod such as an R-D optimization, the number of variations for trialcalculations decreases and it is expected that the amount of processingfor decoding decreases while the degradation of decoding efficiency isinhibited. Moreover, the decoder intentionally biases the generationfrequency of the information relating to a block partitioning direction.This increases accuracy in probability estimation in arithmetic decodingusing a context, such as CABAD, and the improvement of decodingperformance can be expected. The decoder is also capable of limiting theappearance of an extremely elongated block, and this in turn makes itpossible to improve subjective image quality.

The one or more predetermined candidates include, for example, acandidate that performs binary splitting on a block having a shorterside and a longer side in such a manner that a ratio of the longer sideto the shorter side further increases.

This enables the decoder to eliminate a block partitioning methodcandidate such that a current block is split into three blocks moreelongated than before the splitting. The decoder is therefore capable ofprohibiting the appearance of an extremely elongated block that ishardly predicted to appear in the process of block partitioning.Therefore, when a decoding mode is determined using an optimizationmethod such as an R-D optimization, the number of variations for trialcalculations decreases and it is expected that the amount of processingfor decoding decreases while the degradation of decoding efficiency isinhibited. Moreover, the decoder intentionally biases the generationfrequency of the information relating to a block partitioning direction.This increases accuracy in probability estimation in arithmetic decodingusing a context, such as CABAD, and the improvement of decodingperformance can be expected. The decoder is also capable of limiting theappearance of an extremely elongated block, and this in turn makes itpossible to improve subjective image quality.

The one or more predetermined candidates include, for example, acandidate that performs ternary splitting on a block having a shorterside and a longer side in such a manner that a ratio of the longer sideto the shorter side further increases.

This enables the decoder to eliminate a block partitioning methodcandidate such that a current block is split into three blocks moreelongated than before the splitting. The decoder is therefore capable ofprohibiting the appearance of an extremely elongated block that ishardly predicted to appear in the process of block partitioning.Therefore, when a decoding mode is determined using an optimizationmethod such as an R-D optimization, the number of variations for trialcalculations decreases and it is expected that the amount of processingfor decoding decreases while the degradation of decoding efficiency isinhibited. Moreover, the decoder intentionally biases the generationfrequency of the information relating to a block partitioning direction.This increases accuracy in probability estimation in arithmetic decodingusing a context, such as CABAD and the improvement of decodingperformance can be expected. The decoder is also capable of limiting theappearance of an extremely elongated block, and this in turn makes itpossible to improve subjective image quality.

For example, an encoding method according to one aspect of the presentdisclosure includes: determining whether a shape of a current block tobe split in an image satisfies a first condition; generating one or moresecond candidates for a block partitioning method by eliminating one ormore predetermined candidates from a plurality of first candidates for ablock partitioning method when the shape of the current block satisfiesthe first condition; selecting a block partitioning method from amongthe one or more second candidates; and splitting the current blockaccording to the block partitioning method selected.

With the encoding method, it is possible to split a current block intoshapes corresponding to shapes obtained by using a block partitioningmethod selected from among candidates for a block partitioning methodgenerated under a given condition by eliminating one or more candidatesfrom a multiple number of candidates for a block partitioning method.Accordingly, with the encoding method, it is possible, under a givencondition, to split the current block into the shapes corresponding tothe shapes obtained by using the block partitioning method efficientlyselected. In addition, the encoding method makes it possible to prohibitthe appearance of a block having a shape corresponding to a shapeobtained by using a block partitioning method candidate that has beeneliminated. Accordingly, when a coding mode is determined using anoptimization method such as an R-D optimization, the number ofvariations for trial calculations decreases and it is expected that theamount of processing for encoding decreases while the degradation ofcoding efficiency is inhibited. Moreover, the generation frequency ofthe information relating to a block partitioning direction isintentionally biased. Thus, accuracy in probability estimation inarithmetic coding using a context, such as CABAC, increases, and theimprovement of encoding performance can be expected.

For example, a decoding method according to one aspect of the presentdisclosure includes: parsing, from an encoded bitstream generated byencoding an image, block partitioning information relating to a blockpartitioning method according to which a current block to be split inthe image is split; and splitting the current block based on the blockpartitioning information parsed. When a shape of the current blocksatisfies a first condition, the block partitioning information isgenerated by (i) generating one or more second candidates for a blockpartitioning method by eliminating one or more predetermined candidatesfrom a plurality of first candidates for a block partitioning method and(ii) selecting a block partitioning method from among the one or moresecond candidates.

With the decoding method, it is possible to split a current block intoshapes corresponding to shapes obtained by using a block partitioningmethod selected from among candidates for a block partitioning methodgenerated under a given condition by eliminating one or more candidatesfrom a multiple number of candidates for a block partitioning method.Accordingly, it is possible, under a given condition, to split thecurrent block into the shapes corresponding to the shapes obtained byusing the block partitioning method efficiently selected. In addition,it is possible with the decoding method to prohibit the appearance of ablock having a shape corresponding to a shape obtained by using a blockpartitioning method candidate that has been eliminated. Therefore, whena decoding mode is determined using an optimization method such as anR-D optimization, the number of variations for trial calculationsdecreases and it is expected that the amount of processing for decodingdecreases while the degradation of decoding efficiency is inhibited.Moreover, the generation frequency of the information relating to ablock partitioning direction is intentionally biased. This increasesaccuracy in probability estimation in arithmetic decoding using acontext, such as CABAD, and the improvement of decoding performance canbe expected.

An encoder according to one aspect of the present disclosure mayinclude, for example, a splitter, an intra predictor, an interpredictor, a loop filter, a transformer, a quantizer, and an entropyencoder.

The splitter may partition a picture into a plurality of blocks. Theintra predictor may perform intra prediction on a block included in theplurality of blocks. The inter predictor may perform inter prediction onthe block. The transformer may transform prediction errors between anoriginal image and a prediction image obtained through the intraprediction or the inter prediction to generate transform coefficients.The quantizer may quantize the transform coefficients to generatequantized coefficients. The entropy encoder may encode the quantizedcoefficients to generate an encoded bitstream. The loop filter may applya filter to a reconstructed image of the block.

Moreover, the encoder may, for example, encode a video including aplurality of pictures.

The splitter may include circuitry and memory. Using the memory, thecircuitry: determines whether a shape of a current block to be split inan image satisfies a first condition; generates one or more secondcandidates for a block partitioning method by eliminating one or morepredetermined candidates from a plurality of first candidates for ablock partitioning method when the shape of the current block satisfiesthe first condition; selects a block partitioning method from among theone or more second candidates; and splits the current block according tothe block partitioning method selected.

A decoder according to one aspect of the present disclosure may include,for example, an entropy decoder, an inverse quantizer, an inversetransformer, an intra predictor, an inter predictor, and a loop filter.

The entropy decoder may parse, from an encoded bitstream, quantizedcoefficients of a block in a picture. The inverse quantizer may inversequantize the quantized coefficients to obtain transform coefficients.The inverse transformer may inverse transform the transform coefficientsto obtain prediction errors. The intra predictor may perform intraprediction on the block. The inter predictor may perform interprediction on the block. The loop filter may apply a filter to areconstructed image generated using a prediction image obtained throughthe intra prediction or the inter prediction and the prediction errors.

Moreover, the decoder may, for example, decode a video including aplurality of pictures.

The decoder may further include a splitter that partitions a pictureinto a plurality of blocks.

The splitter may include circuitry and memory. Using the memory, thecircuitry: parses, from an encoded bitstream generated by encoding animage, block partitioning information relating to a block partitioningmethod according to which a current block to be split in the image issplit; and splits the current block based on the block partitioninginformation parsed. When a shape of the current block satisfies a firstcondition, the block partitioning information is generated by (i)generating one or more second candidates for a block partitioning methodby eliminating one or more predetermined candidates from a plurality offirst candidates for a block partitioning method and (ii) selecting ablock partitioning method from among the one or more second candidates.

General or specific aspects of the present disclosure may be realized asa system, method, integrated circuit, computer program,computer-readable medium such as a CD-ROM, or any given combinationthereof.

Hereinafter, embodiments will be described with reference to thedrawings.

Note that the embodiments described below each show a general orspecific example. The numerical values, shapes, materials, components,the arrangement and connection of the components, steps, order of thesteps, etc. that are indicated in the following embodiments are mereexamples, and therefore are not intended to limit the scope of theclaims. Moreover, among the components in the following embodiments,those not recited in any of the independent claims defining the broadestinventive concepts are described as optional components.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according toEmbodiment 1, substituting a component corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented processesperformed by one or more components included in the encoder or thedecoder according to Embodiment 1, such as addition, substitution, orremoval, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processcorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosure;

(4) combining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) combining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1 , encoder 100 is a device that encodes apicture block by block, and includes splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, block memory 118, loop filter120, frame memory 122, intra predictor 124, inter predictor 126, andprediction controller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2 , the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2 , block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2 , one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3 , N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO) filter, and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPL 1).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6 , in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7 , in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper regions and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8 , (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.

MATH. 1

∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

$\begin{matrix}{{MATH}.2} &  \\\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0_{x}}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0_{y}}} \right)}{w}y} + v_{0_{x}}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0_{y}}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0_{x}}} \right)}{w}y} + v_{0_{y}}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing. First, an MV is extracted for obtaining, from an encodedreference picture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10 , decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

Inverse Quantized

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type. Moreover, for example, when information parsedfrom an encoded bitstream indicates application of NSST, inversetransformer 206 applies a secondary inverse transform to the transformcoefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

This aspect may be implemented in combination with at least one or moreof the other aspects according to the present disclosure. In addition,one or more of the processes in the flowcharts, one or more of theconstituent elements of the apparatuses, and part of the syntaxdescribed in this aspect may be implemented in combination with otheraspects.

[Internal Configuration of Block Splitter in Encoder According to FirstAspect]

FIG. 11 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to a first aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S1001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Subsequently, encoder 100 determines whether the shape of a currentblock to be split satisfies a first condition (S1002). The firstcondition may be, for example, whether a value indicating a ratio of thelonger side to the shorter side of the current block is greater than apredetermined value.

When the shape of the current block satisfies the first condition (Yesin S1002), encoder 100 eliminates one or more predetermined blockpartitioning method candidates from the first candidates including aplurality of candidates for a block partitioning method (S1003). Acandidate to be eliminated from the first candidates may be, forexample, a candidate corresponding to a block partitioning method suchthat a value indicating a ratio of the longer side to the shorter sideof a block generated through the splitting of a current block is greaterthan a value indicating a ratio of the longer side to the shorter sideof the current block. Specifically, encoder 100 may eliminate binarysplitting in a vertical direction and ternary splitting in a verticaldirection performed on a vertically elongated current block. Note thatthe examples of a candidate to be eliminated from the first candidatesare not limited to those listed above.

By thus eliminating the block partitioning methods as described above,encoder 100 may generate second candidates including one or more blockpartitioning method candidates.

When the shape of the current block does not satisfy the first condition(No in S1002), encoder 100 does not eliminate any block partitioningmethod candidate from the first candidates. Here, candidates generatedby encoder 100 without eliminating any block partitioning methodcandidate from the first candidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate fromamong the second candidates for a block partitioning method (S1004).Even when encoder 100 selects one block partitioning method from thesecond candidates, candidates generated by encoder 100 withouteliminating any block partitioning method candidate from the firstcandidates may be defined as second candidates. An R-D optimization, forinstance, may be used as a method for selecting a block partitioningmethod. The R-D optimization is assumed to be a method in which encoder100 tries out all of a plurality of block partitioning methodcandidates, evaluates the cost of each candidate, and selects a blockpartitioning method candidate that gained the highest score in the costevaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S1004.

It should be noted that in the process performed in step S1003, theelimination of a block partitioning method candidate may be carried outwithout depending on a block partitioning method of a current block tobe split and the number of partitions according to the blockpartitioning method. For example, a block partitioning method candidateto be eliminated from the first candidates may be determined accordingto the type of a picture such as I-picture, P-picture, and B-picture, orthe type of a prediction mode such as intra prediction mode and interprediction mode. Alternatively, a block partitioning method candidate tobe eliminated from the first candidates may be determined using one ofthe following: a block partitioning method of a current block to besplit; and the number of partitions according to the block partitioningmethod.

The process illustrated in FIG. 11 may be applied to the blockpartitioning of a prediction unit (PU) or a transform unit (TU).

[Examples of Block Partitioning Method]

FIG. 12 is a diagram illustrating examples of a block partitioningmethod. The block partitioning method may comprise, for example, quadsplitting of splitting a current block into symmetric quadrilaterals,ternary splitting of splitting a current block with the ratio of 1:2:1in the same direction, and binary splitting of splitting a current blockwith the ratio of 1:1.

Quad splitting 301 of splitting a current block into symmetricquadrilaterals can be expressed as not involving a direction related toblock partitioning because blocks generated through the splitting of thecurrent block are bilaterally and vertically symmetrical.

In the ternary splitting of a current block, the shape of blocksgenerated through the splitting of the current block varies according tothe direction, e.g., vertical, horizontal, etc., in which the splittingis performed on the current block. The ternary splitting comprises, forexample, ternary splitting 302 of splitting a current block into threein a horizontal direction and ternary splitting 303 of splitting acurrent block into three in a vertical direction. Accordingly, theternary splitting is expressed as involving a direction related to blockpartitioning.

When a current block is split into two, the shape of blocks generatedthrough the splitting of the current block varies according to thedirection, e.g., vertical, horizontal, etc., in which the splitting isperformed on the current block. The binary splitting comprises, forexample, binary splitting 304 of splitting a current block into two in ahorizontal direction and binary splitting 305 of splitting a currentblock into two in a vertical direction. Accordingly, the binarysplitting is expressed as involving a direction related to blockpartitioning.

It is to be noted that a partitioning method other than binary splittingand ternary splitting is expressed as involving a direction related toblock partitioning when the shape of blocks generated through thesplitting of a current block varies according to the direction, e.g.,vertical, horizontal, etc., in which the splitting is performed.

The shape of a current block is not limited to a square and may be arectangle, for instance.

Moreover, when splitting a current block into two or three, encoder 100may hold block-partitioning-related direction information which isinformation on a direction related to block partitioning. The case whereencoder 100 holds the block-partitioning-related direction informationis not limited to binary or ternary splitting. The case where encoder100 holds block-partitioning-related direction information may compriseall of cases where the shape of a block generated through the splittingof a current block varies according to the direction in which thecurrent block is split.

FIG. 13 is a diagram illustrating an example of a syntax tree indicatinginformation on a block partitioning method. FIG. 13 shows a syntax treeindicating block partitioning method information, which has, as blockpartitioning method candidates, a selection of binary splitting, ternarysplitting, quad splitting, and no splitting.

First, S that is information indicating whether to perform splitting ispresented. Next, QT that is information indicating whether to performquad splitting is presented. Then, TT that is information indicatingwhether to perform ternary splitting is presented. Lastly, Ver which isinformation indicating a partitioning direction is presented. Wheninformation is set to perform QT, information may be set to perform QTagain. In such a case, a recursive return from QT to QT is allowed inthe syntax tree.

The following describes the case where S=1 is presented, QT=1 ispresented two times, TT=0 is presented, and Ver=0 is presented. Encoder100 firstly performs quad splitting to split a current block into foursymmetrical quadrilaterals. Subsequently, encoder 100 further splitseach of blocks generated through the splitting of the current block intofour symmetrical quadrilaterals. In other words, encoder 100 recursivelysplits the current block into four symmetrical quadrilaterals for twotimes. After that, encoder 100 may perform binary splitting in ahorizontal direction on a block generated through the splittingdescribed above.

Concrete Example 1 of Encoding Process According to First Aspect

FIG. 14 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 1 of the first aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S2001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

First, encoder 100 determines whether the shape of a current block to besplit is a rectangle (S2002). Rectangle may be a vertically elongatedrectangle or a horizontally elongated rectangle. A vertically elongatedrectangle means a rectangle having sides along a vertical directionlonger than sides along a horizontal direction. A horizontally elongatedrectangle means a rectangle having sides along a horizontal directionlonger than sides along a vertical direction. Note that a condition fordetermining the shape of the current block may be whether the currentblock is a square.

When the shape of the current block is a rectangle (Yes in S2002),encoder 100 eliminates, from the first candidates, at least one blockpartitioning method candidate such that a value indicating a ratio ofthe longer side to the shorter side of a block generated through thesplitting of the current block is greater than a value indicating aratio of the longer side to the shorter side of the current block(S2003).

For example, regarding candidates for a block partitioning methodinvolving a direction related to block partitioning, such as ternarysplitting 302 of splitting a current block into three in a horizontaldirection, ternary splitting 303 of splitting a current block into threein a vertical direction, binary splitting 304 of splitting a currentblock into two in a horizontal direction, and binary splitting 305 ofsplitting a current block into two in a vertical direction, a candidatecorresponding to a partitioning method such that the shorter side of avertically elongated block is made shorter or a candidate correspondingto a partitioning method such that the shorter side of a horizontallyelongated block is made shorter may be eliminated.

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

When the shape of the current block is not a rectangle (No in S2002),encoder 100 does not eliminate any block partitioning method candidatefrom the first candidates. Here, candidates generated by encoder 100without eliminating any block partitioning method candidate from thefirst candidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate fromamong the second candidates for a block partitioning method (S2004).Here, encoder 100 may select one block partitioning method candidatefrom among the second candidates. An R-D optimization, for instance, maybe used as a method for selecting a block partitioning method. The R-Doptimization is assumed to be a method in which encoder 100 tries outall of a plurality of block partitioning method candidates, evaluatesthe cost of each candidate, and selects a block partitioning methodcandidate that gained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S2004.

FIG. 15 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 1 of the first aspect. When the shape of a current block to besplit is a square, the current block is splittable in both vertical andhorizontal directions. None of ternary splitting 306 of splitting acurrent block into three in a horizontal direction, ternary splitting307 of splitting a current block into three in a vertical direction,binary splitting 308 of splitting a current block into two in ahorizontal direction, and binary splitting 309 of splitting a currentblock into two in a vertical direction is prohibited or eliminated fromblock partitioning method candidates by encoder 100.

When the shape of the current block is a rectangle, encoder 100 mayeliminate, from the first candidates for a block partitioning method, acandidate corresponding to a partitioning method such that the shorterside of a vertically elongated block is made shorter or a candidatecorresponding to a partitioning method such that the shorter side of ahorizontally elongated block is made shorter.

For example, encoder 100 prohibits ternary splitting 310 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter. On the contrary, encoder 100 does notprohibit ternary splitting 311 of splitting a horizontally elongatedrectangle such that sides along a horizontal direction are made shorter.

In other words, encoder 100 eliminates ternary splitting 310 but doesnot eliminate ternary splitting 311 from the first candidates.

For example, encoder 100 prohibits binary splitting 312 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter. On the contrary, encoder 100 does notprohibit binary splitting 313 of splitting a horizontally elongatedrectangle such that sides along a horizontal direction are made shorter.

In other words, encoder 100 eliminates binary splitting 312 but does noteliminate binary splitting 313 from the first candidates.

[Transition of Candidates for Block Partitioning Direction in ConcreteExample 1 of Encoding Process According to the First Aspect]

FIG. 16 is a flowchart illustrating a process of selecting a blockpartitioning method candidate when a current block to be split is ahorizontally elongated rectangle, according to concrete example 1 of thefirst aspect.

First, encoder 100 generates first candidates for a block partitioningmethod for a current block to be split (S3001). The first candidates mayinclude, for example, a method of performing binary splitting in avertical direction, a method of performing binary splitting in ahorizontal direction, a method of performing ternary splitting in avertical direction, a method of performing quad splitting, and a methodin which no splitting is performed. Note that the block partitioningmethods included in the first candidates are not limited to those listedabove.

Next, encoder 100 determines whether the shape of the current block is arectangle (S3002).

When the shape of the current block is a rectangle (Yes in S3002),encoder 100 eliminates, from the first candidates including a pluralityof block partitioning methods, at least one block partitioning methodcandidate such that a value indicating a ratio of the longer side to theshorter side of a block generated through the splitting of the currentblock is greater than a value indicating a ratio of the longer side tothe shorter side of the current block. For example, a partitioningmethod of performing binary splitting on a horizontally elongatedrectangle in a horizontal direction and a partitioning method ofperforming ternary splitting on a horizontally elongated rectangle in ahorizontal direction are eliminated.

By thus eliminating the block partitioning methods, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

When the shape of the current block is not a rectangle (No in S3002), noblock partitioning method candidate is eliminated from the firstcandidates. Here, candidates generated by encoder 100 withouteliminating any block partitioning method candidate from the firstcandidates may be defined as second candidates.

Encoder 100 then selects a block partitioning method candidate from thesecond candidates for a block partitioning method (S3004). Here, amethod of performing binary splitting in a vertical direction on acurrent block to be split, for example, is selected.

As described above, either or both of the elimination and selection of ablock partitioning method candidate for a current block to be splitis/are performed.

Concrete Example 2 of Encoding Process According to First Aspect

FIG. 17 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by the block splitterin the encoder according to the first aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S4001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether the shape of a current block to besplit is a rectangle (S4002). A condition for determining the shape ofthe current block may be whether the shape of the current block is asquare.

When the shape of the current block is a rectangle (Yes in S4002),encoder 100 eliminates, from the first candidates including a pluralityof block partitioning method candidates, a block partitioning methodcandidate corresponding to ternary splitting such that a valueindicating a ratio of the longer side to the shorter side of a blockgenerated through the splitting of the current block is greater than avalue indicating a ratio of the longer side to the shorter side of thecurrent block (S4003).

For example, a partitioning method of performing ternary splitting on avertically elongated rectangle in a vertical direction and apartitioning method of performing ternary splitting on a horizontallyelongated rectangle in a horizontal direction may be eliminated. Here, ablock partitioning method candidate of performing binary splitting on acurrent block may not be eliminated.

A block partitioning method candidate that performs binary splitting ona current block to be split may be eliminated, but a block partitioningmethod candidate that performs ternary splitting on a current block maynot be eliminated from the first candidates.

By thus eliminating the block partitioning method(s) as described above,encoder 100 may generate second candidates including one or more blockpartitioning method candidates.

When the shape of the current block is not a rectangle (No in S4002), noblock partitioning method candidate is eliminated from the firstcandidates.

Here, candidates generated by encoder 100 without eliminating any blockpartitioning method candidate from the first candidates may be definedas second candidates.

Next, encoder 100 selects a block partitioning method candidate from thesecond candidates for a block partitioning method (S4004). Here, encoder100 may select one block partitioning method candidate from among thesecond candidates. An R-D optimization, for instance, may be used as amethod for selecting a block partitioning method. The R-D optimizationis assumed to be a method in which encoder 100 tries out all of aplurality of block partitioning method candidates, evaluates the cost ofeach candidate, and selects a block partitioning method candidate thatgained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S4004.

Although it is described that encoder 100 eliminates, at step S4003, ablock partitioning method candidate of performing ternary splitting suchthat a value indicating a ratio of the longer side to the shorter sideof a block generated through the splitting of the current block isgreater than a value indicating a ratio of the longer side to theshorter side of the current block, encoder 100 may eliminate a blockpartitioning method candidate of performing binary splitting such that avalue indicating a ratio of the longer side to the shorter side of ablock generated through the splitting of the current block is greaterthan a value indicating a ratio of the longer side to the shorter sideof the current block.

FIG. 18 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 2 of the first aspect. When the shape of a current block to besplit is a square, the current block is splittable in both vertical andhorizontal directions. None of ternary splitting 306 of splitting acurrent block into three in a horizontal direction, ternary splitting307 of splitting a current block into three in a vertical direction,binary splitting 308 of splitting a current block into two in ahorizontal direction, and binary splitting 309 of splitting a currentblock into two in a vertical direction is prohibited or eliminated fromblock partitioning method candidates by encoder 100.

When the shape of the current block is a rectangle, encoder 100 mayeliminate, from the first candidates for a block partitioning method, acandidate corresponding to a partitioning method of performing ternarysplitting on a vertically elongated block such that the shorter sides ofthe block are made shorter or a candidate corresponding to apartitioning method of performing ternary splitting on a horizontallyelongated block such that the shorter sides of the block are madeshorter.

For example, encoder 100 prohibits ternary splitting 310 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter. On the contrary, encoder 100 does notprohibit ternary splitting 311 of splitting a horizontally elongatedrectangle such that sides along a horizontal direction are made shorter.

In other words, encoder 100 eliminates ternary splitting 310, but doesnot eliminate ternary splitting 311 from the first candidates.

For example, encoder 100 neither prohibits binary splitting 312 ofsplitting a horizontally elongated rectangle such that sides along avertical direction are made shorter nor binary splitting 313 ofsplitting a horizontally elongated rectangle such that sides along ahorizontal direction are made shorter.

In other words, encoder 100 eliminates neither binary splitting 312 norbinary splitting 313 from the first candidates.

Concrete Example 3 of Encoding Process According to First Aspect

FIG. 19 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 3 of the first aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S5001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether a value indicating a ratio of thelonger side to the shorter side of a current block to be split isgreater than 2 (S5002).

When the value is greater than 2 (Yes in S5002), encoder 100 eliminates,from the first candidates, a candidate corresponding to a partitioningmethod such that a value indicating a ratio of the longer side to theshorter side of a block generated through the splitting of the currentblock is greater than a value indicating a ratio of the longer side tothe shorter side of the current block (S5003).

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

The following describes the case where binary or ternary splitting whichis splitting that involves a direction related to block partitioning isperformed when the ratio of the longer side to the shorter side of thecurrent block is greater than 2, for example. In this case, a candidatecorresponding to a partitioning method of splitting a horizontallyelongated rectangle such that sides along a vertical direction are madeshorter and a candidate corresponding to a partitioning method ofsplitting a vertically elongated rectangle such that sides along ahorizontal direction are made shorter may be eliminated from the firstcandidates.

When the value indicating the ratio of the longer side to the shorterside of the current block is smaller than or equal to 2 (No in S5002),no block partitioning method candidate is eliminated from the firstcandidates including a plurality of block partitioning methodcandidates. Here, candidates generated by encoder 100 withouteliminating any block partitioning method candidate from the firstcandidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate from thesecond candidates for a block partitioning method (S5004). Here, encoder100 may select one block partitioning method candidate from among thesecond candidates. An R-D optimization, for instance, may be used as amethod for selecting a block partitioning method. The R-D optimizationis assumed to be a method in which encoder 100 tries out all of aplurality of block partitioning method candidates, evaluates the cost ofeach candidate, and selects a block partitioning method candidate thatgained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S5004.

Although it is described that encoder 100 determines, at step S5002,whether the value indicating a ratio of the longer side to the shorterside of the current block is greater than 2, a value used for thedetermination by the encoder is not limited to 2. For example, encoder100 may determine whether the value indicating the ratio of the longerside to the shorter side of the current block is greater than 4.Moreover, the value indicating the ratio of the longer side to theshorter side of the current block, which is used by encoder 100 for thedetermination at step S5002, may be any natural number.

FIG. 20 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 3 of the first aspect.

When the shape of a current block to be split is a square, the currentblock is splittable in both vertical and horizontal directions. None ofternary splitting 306, ternary splitting 307, binary splitting 308, andbinary splitting 309 is prohibited by encoder 100.

In other words, encoder 100 does not eliminate, from the firstcandidates, block partitioning method candidates corresponding toternary splitting 306, ternary splitting 307, binary splitting 308, andbinary splitting 309.

When the value indicating the ratio of the longer side to the shorterside of the current block is smaller than or equal to 2, neither a blockpartitioning method in a vertical direction nor a block partitioningmethod in a horizontal direction is prohibited. For example, any of thefollowing is not prohibited: ternary splitting 314 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter; ternary splitting 315 of splitting ahorizontally elongated rectangle such that sides along horizontaldirection are made shorter; binary splitting 316 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter; and binary splitting 317 of splitting ahorizontally elongated rectangle such that sides along a horizontaldirection are made shorter.

In other words, encoder 100 does not eliminate, from the firstcandidates, block partitioning method candidates corresponding toternary splitting 314, ternary splitting 315, binary splitting 316, andbinary splitting 317.

When the value indicating the ratio of the longer side to the shorterside of the current block is greater than 2, a partitioning method ofsplitting a horizontally elongated rectangle such that sides along avertical direction are made shorter is prohibited. A partitioning methodof splitting a vertically elongated rectangle such that sides along ahorizontal direction are made shorter is also prohibited. For example,ternary splitting 318 of splitting a horizontally elongated rectanglesuch that sides along a vertical direction are made shorter isprohibited, whereas ternary splitting 319 of splitting a horizontallyelongated rectangle such that sides along a horizontal direction aremade shorter is not prohibited. Binary splitting 320 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter is prohibited, whereas binary splitting 321of splitting a horizontally elongated rectangle such that sides along ahorizontal direction are made shorter is not prohibited.

In other words, encoder 100 eliminates, from the first candidates, blockpartitioning method candidates corresponding to ternary splitting 318and binary splitting 320. Moreover, encoder 100 does not eliminate, fromthe first candidates, block partitioning method candidates correspondingto ternary splitting 319 and binary splitting 321.

Concrete Example 4 of Encoding Process According to First Aspect

FIG. 21 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 4 of the first aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S6001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether the shape of a current block to besplit is a rectangle and the length of the shorter side of the currentblock is less than 32 pixels (S6002).

When the shape of the current block is a rectangle and the length of theshorter side of the current block is less than 32 pixels (Yes in S6002),encoder 100 eliminates, from the first candidates, a block partitioningmethod candidate such that a value indicating a ratio of the longer sideto the shorter side of a block generated through the splitting of thecurrent block is greater than a value indicating a ratio of the longerside to the shorter side of the current block (S6003).

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

In the case where the shape of a current block to be split is not asquare and the length of the shorter side is less than 32 pixels whenbinary splitting or ternary splitting that involves a direction relatedto block partitioning is performed, for example, a candidatecorresponding to a partitioning method of splitting a horizontallyelongated rectangle such that sides along a vertical direction are madeshorter and a candidate corresponding to a partitioning method ofsplitting a vertically elongated rectangle such that sides along ahorizontal direction are made shorter are eliminated from the firstcandidates.

When the shape of the current block is not a rectangle or the length ofthe shorter side of the current block is greater than or equal to 32pixels (No in S6002), no block partitioning method candidate iseliminated from the first candidates including a plurality of blockpartitioning method candidates. Here, candidates generated by encoder100 without eliminating any block partitioning method candidate from thefirst candidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate from thesecond candidates for a block partitioning method (S6004). Here, encoder100 may select one block partitioning method candidate from among thesecond candidates. An R-D optimization, for instance, may be used as amethod for selecting a block partitioning method. The R-D optimizationis assumed to be a method in which encoder 100 tries out all of aplurality of block partitioning method candidates, evaluates the cost ofeach candidate, and selects a block partitioning method candidate thatgained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S6004.

Although encoder 100 determines, at step S6002, whether the length ofthe shorter side of the current block is less than 32 pixels, but thelength to be used for the determination is not limited to 32 pixels. Forexample, encoder 100 may determine whether the shorter side of thecurrent block is less than 64 pixels. The length of the shorter side tobe used for the determination may be determined according to a picturesize. A numerical value indicating the length of the shorter side to beused by encoder 100 in the determination at step S6002 may be anynatural number.

FIG. 22 is a chart illustrating block partitioning methods and alimiting condition when splitting is performed, according to concreteexample 4 of the first aspect. When the shape of the current block is asquare, the current block is splittable in both vertical and horizontaldirections. None of ternary splitting 306, ternary splitting 307, binarysplitting 308, and binary splitting 309 is prohibited by encoder 100.

In other words, encoder 100 does not eliminate, from the firstcandidates, block partitioning method candidates corresponding toternary splitting 306, ternary splitting 307, binary splitting 308, andbinary splitting 309.

When the shape of the current block is not a square and the length ofthe shorter side of the current block is greater than or equal to 32pixels, neither a block partitioning method in a vertical direction nora block partitioning method in a horizontal direction is prohibited. Forexample, any of the following is not prohibited: ternary splitting 322of splitting a horizontally elongated rectangle such that sides along avertical direction are made shorter; ternary splitting 323 of splittinga horizontally elongated rectangle such that sides along horizontaldirection are made shorter; binary splitting 325 of splitting ahorizontally elongated rectangle such that sides along a horizontaldirection are made shorter; binary splitting 326 of splitting ahorizontally elongated rectangle such that sides along a horizontaldirection are made shorter; and binary splitting 327 of splitting avertically elongated rectangle such that sides along a horizontaldirection are made shorter.

In other words, encoder 100 does not eliminate, from the firstcandidates, block partitioning method candidates corresponding toternary splitting 322, ternary splitting 323, binary splitting 324,binary splitting 325, binary splitting 326, and binary splitting 327.

When the shape of the current block is not a square and the length ofthe shorter side is less than 32 pixels, a partitioning method ofsplitting a horizontally elongated rectangle such that sides along avertical direction are made shorter is prohibited. A partitioning methodof splitting a vertically elongated rectangle such that sides along ahorizontal direction are made shorter is also prohibited. For example,ternary splitting 328 of splitting a horizontally elongated rectanglesuch that sides along a vertical direction are made shorter isprohibited, whereas ternary splitting 329 of splitting a horizontallyelongated rectangle such that sides along a vertical direction are madeshorter is not prohibited. Binary splitting 330 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter is prohibited, whereas binary splitting 331of splitting a horizontally elongated rectangle such that sides along ahorizontal direction are made shorter is not prohibited.

In other words, encoder 100 eliminates, from the first candidates, blockpartitioning method candidates corresponding to ternary splitting 328and binary splitting 330. Moreover, encoder 100 does not eliminate, fromthe first candidates, block partitioning method candidates correspondingto ternary splitting 329 and binary splitting 331.

Concrete Example 5 of Encoding Process According to First Aspect

FIG. 23 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 5 of the first aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S7001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether a value indicating a ratio of thelonger side to the shorter side of a block generated through thesplitting of a current block is greater than a third value (S7002). Thethird value may be, for example, 4 or 8. The third value may be anynatural number.

When the value is greater than the third value (Yes in S7002), encoder100 eliminates, from the first candidates, a candidate corresponding toa block partitioning method such that the value indicating the ratio ofthe longer side to the shorter side of the block generated through thesplitting of the current block increases to be greater than the thirdvalue (S7003).

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

When the value is smaller than or equal to the third value (No inS7002), no block partitioning method candidate is eliminated from thefirst candidates including a plurality of block partitioning methodcandidates. Here, candidates generated by encoder 100 withouteliminating any block partitioning method candidate from the firstcandidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate from thesecond candidates for a block partitioning method (S7004). Here, encoder100 may select one block partitioning method candidate from among thesecond candidates. An R-D optimization, for instance, may be used as amethod for selecting a block partitioning method. The R-D optimizationis assumed to be a method in which encoder 100 tries out all of aplurality of block partitioning method candidates, evaluates the cost ofeach candidate, and selects a block partitioning method candidate thatgained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S7004.

FIG. 24 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 5 of the first aspect. When avalue indicating a ratio of the longer side to the shorter side of acurrent block to be split is smaller than 2, the current block issplittable in both vertical and horizontal directions. None of binarysplitting 332 of splitting a current block into two in a horizontaldirection, binary splitting 333 of splitting a current block into two ina vertical direction, ternary splitting 334 of splitting a current blockinto three in a horizontal direction, and ternary splitting 335 ofsplitting a current block into three in a vertical direction isprohibited by encoder 100.

In other words, encoder 100 does not eliminate, from the firstcandidates, block partitioning method candidates corresponding to binarysplitting 332, binary splitting 333, ternary splitting 334, and ternarysplitting 335.

When the value indicating the ratio of the longer side to the shorterside of the current block is greater than or equal to 2 and smaller than4, binary splitting 336 of splitting a horizontally elongated rectanglesuch that sides along a horizontal direction are made shorter, ternarysplitting 337 of splitting a horizontally elongated rectangle such thatsides along a horizontal direction are made shorter, and binarysplitting 338 of splitting a horizontally elongated rectangle such thatsides along a vertical direction are made shorter are not prohibited. Onthe contrary, ternary splitting 339 of splitting a horizontallyelongated rectangle such that sides along a vertical direction are madeshorter is prohibited. In ternary splitting 339, the ratio of theshorter side to be split may be 1:2:1.

In other words, encoder 100 does not eliminate, from the firstcandidates, block partitioning method candidates corresponding to binarysplitting 36, ternary splitting 37, and binary splitting 38. Incontrast, encoder 100 eliminates, from the first candidates, a blockpartitioning method candidate corresponding to ternary splitting 339.

When the value indicating the ratio of the longer side to the shorterside of the current block is greater than or equal to 4, binarysplitting 340 of splitting a horizontally elongated rectangle such thatsides along a horizontal direction are made shorter, ternary splitting341 of splitting a horizontally elongated rectangle such that sidesalong a horizontal direction are made shorter are not prohibited byencoder 100. In contrast, binary splitting 342 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter and ternary splitting 343 of splitting ahorizontally elongated rectangle such that sides along a verticaldirection are made shorter are prohibited by encoder 100.

In other words, encoder 100 does not eliminate, from the firstcandidates, block partitioning method candidates corresponding to binarysplitting 340 and ternary splitting 341. In contrast, encoder 100eliminates, from the first candidates, block partitioning methodcandidates corresponding to ternary splitting 342 and ternary splitting343.

Advantageous Effects of First Aspect

With the configuration according to the first aspect, it is predictedthat an extremely elongated block is hardly generated in the splittingof a current block by splitter 102 in encoder 100. Accordingly, it ispossible to reduce the number of block partitioning methods to beselected in the present processing by prohibiting in advance a blockpartitioning method that generates a shape that is most unlikely to begenerated. This reduces the number of block partitioning methodstargeted for calculation when encoder 100 determines a coding mode usingoptimization such as an R-D optimization, for instance. Encoder 100therefore is capable of reducing the amount of processing necessary forencoding while inhibiting the degradation of coding efficiency.

Moreover, with the encoder intentionally biasing the generationfrequency of each piece of information on a direction related to blockpartitioning, accuracy in probability estimation in arithmetic codingusing a context increases. The arithmetic coding using a context is, forexample, CABAC. Accordingly, by performing the processes described inthe present disclosure, coding performance may be improved.

Note that the encoder, decoder, the encoding method, and the decodingmethod according to the present disclosure do not always need to includeall of the elements described in the first aspect, and may include onlyone or more of the elements. Moreover, each of the determinationconditions according to the first aspect may be the same as thecorresponding one of those described in the concrete examplesillustrated in the first aspect, or may be any combination of thosedescribed in the concrete examples illustrated in the first aspect. Eachof the numerical values used for determination conditions in the firstaspect may be modified.

With encoder 100 inhibiting the appearance of an extremely elongatedblock, subjective image quality may be improved.

It should be noted that the term “elongated” used herein may mean that aratio of the longer side to the shorter side or a difference between thelonger side and the shorter side of a block is greater than or equal toa predetermined value. The predetermined value may be, for example, 2, 4or 8. The phrase “a current block is split into shapes each being moreelongated than before the splitting” may mean that a ratio of the longerside to the shorter side or a difference between the longer side and theshorter side of a block generated through the splitting increases due tothe splitting of the current block. The block according to the presentdisclosure is not limited to a rectangular block.

[Internal Configuration of Block Splitter in Encoder According to SecondAspect]

FIG. 25 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to a second aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S8001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether the shape of a current block to besplit satisfies a predetermined condition (S8002).

When the shape of the current block satisfies the predeterminedcondition (Yes in S8002), encoder 100 eliminates a predetermined blockpartitioning method candidate from the first candidates (S8003).

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

When the shape of the current block does not satisfy the predeterminedcondition (No in S8002), no block partitioning method candidate iseliminated from the first candidates including a plurality of blockpartitioning method candidates. Here, the candidates generated byencoder 100 without eliminating any block partitioning method candidatefrom the first candidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate fromamong the second candidates for a block partitioning method (S8004).Here, encoder 100 may select one block partitioning method candidatefrom among the second candidates. An R-D optimization, for instance, maybe used as a method for selecting a block partitioning method. The R-Doptimization is assumed to be a method in which encoder 100 tries outall of a plurality of block partitioning method candidates, evaluatesthe cost of each candidate, and selects a block partitioning methodcandidate that gained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S8004.

Next, encoder 100 encodes block partitioning information that is notuniquely determined (S8005). The encoding performed by encoder 100includes an encoding process and writing of encoded information into abitstream.

The process in step S8005 may be performed when block partitioninginformation is not uniquely determined based on the shape of a currentblock to be split, and prohibited in other cases. For example, whennothing but splitting a rectangular current block such that a valueindicating a ratio of the longer side to the shorter side of a blockgenerated through the splitting decreases is performed, the process instep S8005 does not need to be performed. Block partitioning informationmay include either or both of a direction related to block partitioningand the number of partitions according to a block partitioning method.

Note that in the process performed in step S8003, the elimination of ablock partitioning method candidate may be carried out without dependingon a block partitioning method of a current block to be split and thenumber of partitions according to the block partitioning method. Forexample, a block partitioning method candidate to be eliminated from thefirst candidates may be determined according to the type of a picturesuch as I-picture, P-picture, and B-picture, or the type of a predictionmode such as intra prediction mode and inter prediction mode.Alternatively, a block partitioning method candidate to be eliminatedfrom the first candidates may be determined using one of the following:a block partitioning method of a current block to be split; and thenumber of partitions according to the block partitioning method.

The process illustrated in FIG. 25 may be applied to the blockpartitioning of a prediction unit (PU) or a transform unit (TU).

Encoder 100 may write a condition used for the determination in stepS8002 into the syntax such as a sequence layer, a picture layer, or aslice layer. Moreover, encoder 100 may write the condition into asequence parameter set (SPS).

Concrete Example 1 of Encoding Process According to Second Aspect

FIG. 26 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 1 of the second aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S9001). A block partitioning method is a method for splitter 102in encoder 100 to split a current block. A current block to be split isan image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether the shape of a current block to besplit satisfies a predetermined condition (S9002).

When the shape of the current block satisfies the predeterminedcondition (Yes in S9002), encoder 100 eliminates a predetermined blockpartitioning method candidate from the first candidates (S9003).

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

When the shape of the current block does not satisfy the predeterminedcondition (No in S9002), no block partitioning method candidate iseliminated from the first candidates including a plurality of blockpartitioning method candidates. Here, candidates generated by encoder100 without eliminating any block partitioning method candidate from thefirst candidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate fromamong the second candidates for a block partitioning method (S9004).Here, encoder 100 may select one block partitioning method candidatefrom among the second candidates. An R-D optimization, for instance, maybe used as a method for selecting a block partitioning method. The R-Doptimization is assumed to be a method in which encoder 100 tries outall of a plurality of block partitioning method candidates, evaluatesthe cost of each candidate, and selects a block partitioning methodcandidate that gained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S9004.

Next, encoder 100 encodes the number of partitions (S9005). The encodingperformed by encoder 100 includes an encoding process and writing ofencoded information into a bitstream.

Subsequently, encoder 100 determines whether the selected blockpartitioning method candidate is a block partitioning method candidateinvolving a direction related to block partitioning (S9006). The blockpartitioning method involving a direction related to block partitioningmay be, for example, binary splitting or ternary splitting.

When the selected block partitioning method candidate is not a blockpartitioning method candidate involving a direction related to blockpartitioning (No in S9006), encoder 100 ends the process.

When the selected block partitioning method candidate is a blockpartitioning method candidate involving a direction related to blockpartitioning (Yes in S9006), encoder 100 determines whether the numberof partitions according to the block partitioning method satisfies apredetermined condition (S9007). The predetermined condition may be, forexample, that the number of partitions according to the blockpartitioning method is equal to the number of partitions obtained by acandidate that has been eliminated from the block partitioning methodcandidates.

When the number of partitions does not satisfy the predeterminedcondition (No in S9007), encoder 100 performs a process in step S9009.The process in step S9009 will be described later.

When the number of partitions satisfies the predetermined condition (Yesin S9007), encoder 100 determines whether the shape of the current blocksatisfies a predetermined condition (S9008). Here, the predeterminedcondition may be the same as the condition used in step S9003 fordetermining whether a block partitioning method candidate is to beeliminated.

When the shape of the current block does not satisfy the predeterminedcondition (No in S9008), encoder 100 encodes block-partitioning-relateddirection information which is information on a direction related toblock partitioning (S9009). The encoding here may include an encodingprocess and writing of encoded information into a bitstream. After theencoding, encoder 100 ends the operation.

When the shape of the current block satisfies the predeterminedcondition (Yes in S9008), encoder 100 ends the process without encodingthe block-partitioning-related direction information.

Note that the concrete examples of a determination condition related tothe shape of a current block to be split and a block partitioning methodcandidate to be eliminated may be the same as those illustrated in thefirst aspect. The order of the processes performed by encoder 100according to the present aspect may be reversed. In other words, encoder100 may change the order of processes according to the shape of a syntaxtree presenting an order of processes. When syntax presenting adirection related to block partitioning is located upper than syntaxregarding the number of partitions according to a block partitioningmethod, for example, the order of step S9006 and step S9007 may bereversed.

FIG. 27 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 2 of the second aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S10001). A block partitioning method is a method for splitter102 in encoder 100 to split a current block. A current block to be splitis an image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether the shape of a current block to besplit is a rectangle (S10002).

When the shape of the current block is a rectangle (Yes in S10002),encoder 100 eliminates, from the first candidates, a block partitioningmethod candidate such that a value indicating a ratio of the longer sideto the shorter side of a block generated through the splitting of thecurrent block further increases to be greater than a value indicating aratio of the longer side to the shorter side of the current block(S10003).

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

When the shape of the current block is not a rectangle (No in S10002),no block partitioning method candidate is eliminated from the firstcandidates including a plurality of block partitioning methodcandidates. Here, candidates generated by encoder 100 withouteliminating any block partitioning method candidate from the firstcandidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate fromamong the second candidates for a block partitioning method (S10004).Here, encoder 100 may select one block partitioning method candidatefrom among the second candidates. An R-D optimization, for instance, maybe used as a method for selecting a block partitioning method. The R-Doptimization is assumed to be a method in which encoder 100 tries outall of a plurality of block partitioning method candidates, evaluatesthe cost of each candidate, and selects a block partitioning methodcandidate that gained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S10004.

Next, encoder 100 encodes the number of partitions (S10005). Theencoding performed by encoder 100 includes an encoding process andwriting of encoded information into a bitstream.

Subsequently, encoder 100 determines whether the selected blockpartitioning method candidate is a block partitioning method candidateinvolving a direction related to block partitioning (S10006). The blockpartitioning method involving a direction related to block partitioningmay be, for example, binary splitting or ternary splitting.

When the selected block partitioning method candidate is not a blockpartitioning method candidate involving a direction related to blockpartitioning (No in S10006), encoder 100 ends the process.

When the selected block partitioning method candidate is a blockpartitioning method candidate involving a direction related to blockpartitioning (Yes in S10006), encoder 100 determines whether the blockpartitioning method is binary splitting or ternary splitting (S10007).

When the block partitioning method is neither binary splitting norternary splitting (No in step S10007), encoder 100 performs a process instep S10009. The process in step S10009 will be described later.

When the block partitioning method is binary splitting or ternarysplitting (Yes in S10007), encoder 100 determines whether the shape ofthe current block is a rectangle (S10008).

When the shape of the current block is not a rectangle (No in S10008),encoder 100 encodes block-partitioning-related direction informationwhich is information on a direction related to block partitioning(S10009). The encoding here may include an encoding process and writingof encoded information into a bitstream. For example, binary splitting305 of splitting a current block into two in a vertical direction isselected from the second candidates. When the shape of the current blockis horizontally elongated, encoder 100 presents S=0, QT=0, and TT=0 in asyntax tree such that illustrated in FIG. 3 and writes syntax into abitstream without using Ver. For example, binary splitting 302 ofsplitting a current block into three in a horizontal direction isselected from the second candidates. When the shape of the current blockis vertically elongated, encoder 100 presents S=0, QT=0, and TT=1 in asyntax tree such that illustrated in FIG. 3 and writes syntax into abitstream without using Ver.

When the shape of the current block is a rectangle (Yes in S10008),encoder 100 ends the process without encoding theblock-partitioning-related direction information.

FIG. 28 is a flowchart illustrating a process of selecting a blockpartitioning method candidate, which is performed by a block splitter inan encoder according to concrete example 3 of the second aspect.

First, encoder 100 generates first candidates for a block partitioningmethod (S11001). A block partitioning method is a method for splitter102 in encoder 100 to split a current block. A current block to be splitis an image block to be split by splitter 102 when encoder 100 performsencoding. The first candidates may include, for example, a method ofperforming binary splitting in a vertical direction, a method ofperforming binary splitting in a horizontal direction, a method ofperforming ternary splitting in a vertical direction, a method ofperforming quad splitting, and a method in which no splitting isperformed. Note that the block partitioning methods included in thefirst candidates are not limited to those listed above.

Next, encoder 100 determines whether the shape of a current block to besplit is a rectangle (S11002).

When the shape of the current block is a rectangle (Yes in S11002),encoder 100 eliminates, from the first candidates, a block partitioningmethod candidate such that a value indicating a ratio of the longer sideto the shorter side of a block generated through the splitting of thecurrent block further increases to be greater than a value indicating aratio of the longer side to the shorter side of the current block(S11003).

By thus eliminating the block partitioning method, encoder 100 maygenerate second candidates including one or more block partitioningmethod candidates.

When the shape of the current block is not a rectangle (No in S11002),no block partitioning method candidate is eliminated from the firstcandidates including a plurality of block partitioning methodcandidates. Here, candidates generated by encoder 100 withouteliminating any block partitioning method candidate from the firstcandidates may be defined as second candidates.

Next, encoder 100 selects a block partitioning method candidate fromamong the second candidates for a block partitioning method (S11004).Here, encoder 100 may select one block partitioning method candidatefrom among the second candidates. An R-D optimization, for instance, maybe used as a method for selecting a block partitioning method. The R-Doptimization is assumed to be a method in which encoder 100 tries outall of a plurality of block partitioning method candidates, evaluatesthe cost of each candidate, and selects a block partitioning methodcandidate that gained the highest score in the cost evaluation.

Encoder 100 then splits the current block according to the blockpartitioning method selected in step S11004.

Next, encoder 101 encodes the number of partitions (S11005). Theencoding performed by encoder 100 includes an encoding process andwriting of encoded information into a bitstream.

Subsequently, encoder 100 determines whether the selected blockpartitioning method candidate is a block partitioning method candidateinvolving a direction related to block partitioning (S11006). The blockpartitioning method involving a direction related to block partitioningmay be, for example, binary splitting or ternary splitting.

When the selected block partitioning method candidate is not a blockpartitioning method candidate involving a direction related to blockpartitioning (No in S11006), encoder 100 ends the process.

When the selected block partitioning method candidate is a blockpartitioning method candidate involving a direction related to blockpartitioning (Yes in S11006), encoder 100 determines whether the blockpartitioning method is ternary splitting (S11007).

When the block partitioning method is not ternary splitting (No inS11007), encoder 110 performs a process in step S11009. The process instep S11009 will be described later.

When the block partitioning method is ternary splitting (Yes in S11007),encoder 100 determines whether the shape of the current block is arectangle (S11008).

When the shape of the current block is not a rectangle (No in S11008),encoder 100 encodes block-partitioning-related direction informationwhich is information on a direction related to block partitioning(S11009). The encoding here may include an encoding process and writingof encoded information into a bitstream. For example, binary splitting305 of splitting a current block into two in a vertical direction isselected from the second candidates. When the shape of the current blockis horizontally elongated, encoder 100 presents S=0, QT=0, TT=0, andVer=1 in a syntax tree such that illustrated in FIG. 3 and writes syntaxinto a bitstream. For example, ternary splitting 302 of splitting acurrent block into three in a horizontal direction is selected from thesecond candidates. When the shape of the current block is verticallyelongated, encoder 100 presents S=0, QT=0, and TT=1 in a syntax treesuch that illustrated in FIG. 3 and writes syntax into a bitstreamwithout using Ver.

When the shape of the current block is a rectangle (Yes in S11008),encoder 100 ends the process without encoding theblock-partitioning-related direction information.

At step S11007, encoder 100 determines whether the number of partitionsaccording to the block partitioning method is three, but may determinewhether the number of partitions is two.

At step S11008, encoder 100 determines whether the shape of the currentblock is a rectangle, but may determine whether a value indicating aratio of the longer side to the shorter side of the current block isgreater than a predetermined value.

[Internal Configuration of Block Splitter in Decoder According to SecondAspect]

FIG. 29 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to the second aspect.

First, decoder 200 refers to the shape of a current block to be split(S12001). A current block to be split is a block to be split by decoder200. Here, decoder 200 may calculate the shape of the current block.

Next, decoder 200 determines whether a block partitioning method is tobe uniquely determined based on the shape of the current block (S12002).

When the block partitioning method is to be uniquely determined based onthe shape of the current block (Yes in S12002), decoder 200 does notrefer to block partitioning information etc.

When the block partitioning method is not to be uniquely determinedbased on the shape of the current block (No in S12002), decoder 200refers to block partitioning information (S12003). In other words,decoder 200 reads out the shape of the current block or blockpartitioning information that is encoded and written into a bitstream byencoder 100.

Next, decoder 200 performs block partitioning according to apredetermined block partitioning method (S12004). The predeterminedblock partitioning method may be a block partitioning method indicatedin the block partitioning information referred to in step S12003. Whenthe block partitioning method is to be uniquely determined in stepS12002, the predetermined block partitioning method may be that blockpartitioning method uniquely determined.

Decoder 200 then ends the operation.

In the process illustrated in FIG. 29 , a block partitioning methodcandidate may be eliminated based on a determination condition otherthan the shape of a current block to be split. For example, a blockpartitioning method candidate to be eliminated from the first candidatesmay be determined according to the type of a picture such as I-picture,P-picture, and B-picture, or the type of a prediction mode such as intraprediction mode and inter prediction mode. Alternatively, a blockpartitioning method candidate to be eliminated from the first candidatesmay be determined using one of the following: a block partitioningmethod of a current block to be split; and the number of partitionsaccording to the block partitioning method.

Concrete Example 1 of Decoding Process According to Second Aspect

FIG. 30 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to concrete example 1 of the secondaspect.

First, decoder 200 refers to information related to the number ofpartitions according to the block partitioning method used for encoding(S13001). Decoder 200 may refer to the information related to the numberof partitions by decoding a bitstream transmitted from encoder 100. Inother words, decoder 200 reads out the shape of a current block to besplit or block partitioning information that is encoded and written intothe bitstream by encoder 100. The information referred to here may be,for example, TT-Flag, QT-Flag, or S-Flag in the syntax tree illustratedin FIG. 13 .

Next, decoder 200 determines whether the block partitioning method is ablock partitioning method candidate corresponding to splitting thatinvolves a direction related to block partitioning (S13002).

When the block partitioning method is not a block partitioning methodcandidate corresponding to splitting that involves a direction relatedto block partitioning (No in S13002), decoder 200 does not refer toblock partitioning information. This applies also to the case, forexample, where block partitioning information is to be uniquelydetermined based on the shape of a current block to be split. This isbecause decoder 200 does not need to refer to information on a directionrelated to block partitioning. Decoder 200 then performs splitting ofthe current block (S13006).

When the block partitioning method is a block partitioning methodcandidate corresponding to splitting that involves a direction relatedto block partitioning (Yes in S13002), decoder 200 determines whetherthe number of partitions is a predetermined number (S13003). Decoder 200may determine, for example, whether the number of partitions is three.

When the number of partitions is not the predetermined number (No inS13003), decoder 200 refers to block-partitioning-related directioninformation which is information on a direction related to blockpartitioning (S13005). Decoder 200 then performs splitting of thecurrent block (S13006).

When the number of partitions is the predetermined number (Yes inS13003), decoder 200 determines whether the shape of the current blocksatisfies a predetermined condition (S13004). The predeterminedcondition here is, for example, whether the shape of the current blockis a rectangle.

When the shape of the current block satisfies the predeterminedcondition (Yes in S13004), decoder 200 performs splitting of the currentblock (S13006). The current block may be split in a predetermineddirection. For example, when the current block is vertically elongated,the current block may be split in a horizontal direction, and when thecurrent block is horizontally elongated, the current block may be splitin a vertical direction.

When the shape of the current block does not satisfy the predeterminedcondition (No in S13004), decoder 200 refers to block partitioninginformation (S13005). Subsequently, decoder 200 splits the current blockbased on the block partitioning information (S13006).

Thus, when the shape of the current block satisfies the predeterminedcondition at step S13006, decoder 200 may split the current blockwithout parsing the block partitioning information.

The block partitioning information may include either or both of adirection related to block partitioning and the number of partitionsaccording to a block partitioning method.

Concrete Example 2 of Decoding Process According to Second Aspect

FIG. 31 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to concrete example 2 of the secondaspect.

First, decoder 200 refers to information related to the number ofpartitions according to the block partitioning method used for encoding(S14001). Decoder 200 may refer to the information related to the numberof partitions by decoding a bitstream transmitted from encoder 100. Inother words, decoder 200 reads out the shape of a current block to besplit or block partitioning information that is encoded and written intoa bitstream by encoder 100. The information referred to here may be, forexample, TT-Flag, QT-Flag, or S-Flag in the syntax tree illustrated inFIG. 13 .

Next, decoder 200 determines whether the block partitioning method is ablock partitioning method candidate corresponding to splitting thatinvolves a direction related to block partitioning (S14002).

When the block partitioning method is not a block partitioning methodcandidate corresponding to splitting that involves a direction relatedto block partitioning (No in S14002), decoder 200 does not refer toblock partitioning information. This is because decoder 200 does notneed to refer to block-partitioning-related information which isinformation on a direction related to block partitioning. Decoder 200then performs splitting of the current block (S14006).

When the block partitioning method is a block partitioning methodcandidate corresponding to splitting that involves a direction relatedto block partitioning (Yes in S14002), decoder 200 determines whetherthe number of partitions is two or three (S14003).

When the number of partitions is neither two nor three (No in S14003),decoder 200 refers to block-partitioning-related direction informationwhich is information on a direction related to block partitioning(S14005). Decoder 200 then performs splitting of the current block(S14006).

When the number of partitions is two or three (Yes in S14003), decoder200 determines whether the shape of the current block is a rectangle(S14004).

When the shape of the current block is a rectangle (Yes in S14004),decoder 200 performs splitting of the current block (S14006). Decoder200 performs the splitting without referring to theblock-partitioning-related direction information. When the number ofpartitions according to the block partitioning method referred to is twoor three, for example, decoder 200 may split a vertically elongatedblock in a horizontal direction or split a horizontally elongated blockin a vertical direction.

When the shape of the current block is not a rectangle (No in S14004),decoder 200 refers to block partitioning information (S14005). Decoder200 then performs splitting of the current block based on the blockpartitioning information (S14006).

At step S14004, decoder 200 determines whether the shape of the currentblock is a rectangle, but may determine whether a value indicating aratio of the longer side to the shorter side of the current block isgreater than a first value. The first value may be 2 or 4. The firstvalue may be any natural number.

At step S14004, decoder 200 determines whether the shape of the currentblock is a rectangle, but may determine whether the shape of the currentblock is a rectangle and a value indicating a ratio of the longer sideto the shorter side of the current block is smaller than a second value.The second value may be, for example, 64 pixels. The second value may bea given number of pixels in a range selectable by encoder 100.

At step S14004, decoder 200 determines whether the shape of the currentblock is a rectangle, but may determine whether a value indicating aratio of the longer side to the shorter side of a block generatedthrough the splitting of the current block is greater than a thirdvalue. The third value may be 4 or 8. The third value may be any naturalnumber.

Concrete Example 3 of Decoding Process According to Second Aspect

FIG. 32 is a flowchart illustrating a process of referring to blockpartitioning information and performing block partitioning, which isperformed by a decoder according to concrete example 3 of the secondaspect.

First, decoder 200 refers to information related to the number ofpartitions in accordance with a block partitioning method (S15001).Decoder 200 may refer to the information related to the number ofpartitions by decoding a bitstream transmitted from encoder 100. Theinformation referred to here may be, for example, TT-Flag, QT-Flag, orS-Flag in the syntax tree illustrated in FIG. 13 .

Next, decoder 200 determines whether the block partitioning methodreferred to is a block partitioning method candidate involving adirection related to block partitioning (S15002).

When the block partitioning method referred to is not a blockpartitioning method candidate involving a direction related to blockpartitioning (No in S15002), decoder 200 does not refer to blockpartitioning information. This is because decoder 200 does not need torefer to block-partitioning-related direction information which isinformation on a direction related to block partitioning. Decoder 200then performs splitting of the current block (S15006).

When the block partitioning method referred to by decoder 200 is a blockpartitioning method candidate involving a direction related to blockpartitioning (Yes in S15002), decoder 200 determines whether the numberof partitions is three (S15003).

When the number of partitions is not three (No in S15003), decoder 200refers to block-partitioning-related direction information (S15005).Decoder 200 then performs splitting of the current block (S15006).

When the number of partitions is three (Yes in S15003), decoder 200determines whether the shape of the current block is a rectangle(S15004).

When the shape of the current block is a rectangle (Yes in S15004),decoder 200 performs splitting of the current block (S15006). Decoder200 performs the splitting without referring to theblock-partitioning-related direction information. For example, when thenumber of partitions according to the block partitioning method referredto is three, decoder 200 may split a vertically elongated block in ahorizontal direction or split a horizontally elongated block in avertical direction.

When the shape of the current block is not a rectangle (No in S15004),decoder 200 refers to block partitioning information (S15005). Decoder200 then splits the current block based on the block partitioninginformation (S15006).

In the process illustrated in FIG. 32 , when information indicating thatternary splitting is to be performed on a horizontally elongated blockis written in a bitstream, for example, decoder 200 may perform ternarysplitting on a current block to be split in a vertical direction withoutreferring to block-partitioning-related direction information. Wheninformation indicating that binary splitting is to be performed on ahorizontally elongated block is written in a bitstream, for example,decoder 200 refers to block-partitioning-related direction informationand performs block partitioning. When the block-partitioning-relateddirection information referred to indicates horizontal splitting,decoder 200 may perform binary splitting on the current block in ahorizontal direction.

Advantageous Effects of Second Aspect

With the configuration according to the second aspect, it is predictedthat an extremely elongated block is hardly generated in the splittingof a current block by splitter 102 in encoder 100. Accordingly, it ispossible to reduce the number of block partitioning methods to beselected in the present processing by prohibiting in advance a blockpartitioning method that generates a shape that is most unlikely to begenerated. This reduces the number of block partitioning methodstargeted for calculation when encoder 100 determines a coding mode usingoptimization such as an R-D optimization, for instance. Encoder 100therefore is capable of reducing the amount of processing necessary forencoding while inhibiting the degradation of coding efficiency. Besides,by additionally skipping the process of writing syntax into a bitstream,the amount of processing necessary for encoding is further reduced.

Moreover, with the encoder intentionally biasing the generationfrequency of each piece of information on a direction related to blockpartitioning, accuracy in probability estimation in arithmetic codingusing a context increases. The arithmetic coding using a context is, forexample, CABAC. Accordingly, by performing the processes described inthe present disclosure, coding performance may be improved.

Moreover, by inhibiting the appearance of an extremely elongated block,subjective image quality may be improved.

Note that the encoder, decoder, the encoding method, and the decodingmethod according to the present disclosure do not always need to includeall of the elements described in the second aspect, and may include onlyone or more of the elements. Moreover, each of the determinationconditions according to the second aspect may be the same as thecorresponding one of those described in the concrete examplesillustrated in the second aspect, or may be any combination of thosedescribed in the concrete examples illustrated in the second aspect.Each of the numerical values used for determination conditions in thesecond aspect may be modified.

Variations

In the process of splitting a current block performed by encoder 100 ordecoder 200, when the structure of a block is set differently betweenchroma signals and luma signals, encoder 100 may use the presentdisclosure for either luma signals or chroma signals.

Encoder 100 or decoder 200 may determine, per slice, whether to executethe processes included in the present disclosure.

Encoder 100 or decoder 200 may determine, per tile, whether to executethe processes included in the present disclosure.

Encoder 100 or decoder 200 may determine, per slice type, whether toexecute the processes included in the present disclosure. A slice typeis, for example, I-slice, P-slice, or B-slice.

The ternary splitting performed on a current block to be split byencoder 100 or decoder 200 does not need to split the block into blocksof equal size. For example, the current block may be split so that thelength of a given side of the block is split with the ratio of 1:2:1.

Encoder 100 or decoder 200 may determine whether to execute theprocesses included in the present disclosure according to a predictionmode.

In the processes performed by encoder 100, a flag indicating that theprocesses included in the present disclosure have been performed intosyntax such as a sequence layer, a picture layer, or a slice layer in abitstream.

Encoder 100 may write information related to the determination conditionused for the processes included in the present disclosure into syntax,in a bitstream, such as a sequence layer, a picture layer, or a slicelayer. The information related to determination condition includes avalue indicating a ratio of the longer side to the shorter side of acurrent block to be split, a value indicating a ratio of the longer sideto the shorter side of a block generated through the splitting of thecurrent block, an absolute value indicating the shorter side of thecurrent block, information on a block partitioning method candidate tobe eliminated, etc.

When the number of partitions according to a block partitioning methodis uniquely determined based on the shape of a current block to besplit, encoder 100 or decoder 200 may skip encoding or decoding ofinformation related to the number of partitions according to the blockpartitioning method. When it is determined that splitting is notperformed on a current block having the size of 8×8, for example,encoder 100 or decoder 200 does not need to perform encoding or decodingof information related to the number of partitions according to theblock partitioning method used for 8×8 blocks.

The concrete examples of the determination conditions used in theprocessed included in the present disclosure are not limited to thosedescribed herein. Moreover, the number of times a process of thedetermination is performed in the processes included in the presentdisclosure may be different from those described in the concreteexamples.

[Implementation]

FIG. 33 is a block diagram illustrating an example of implementation ofencoder 100. Encoder 100 includes processing circuitry 150 and memory152. For example, the elements of encoder 100 illustrated in FIG. 1 areimplemented by processing circuitry 150 and memory 152 illustrated inFIG. 33 .

Circuitry 150 is an electronic circuit accessible to memory 152 andprocesses information. For example, processing circuitry 152 is adedicated or general-purpose electronic circuit which encodes videosusing memory 152. Circuitry 260 may be a processor such as a CPU.Circuitry 150 may be an aggregate of a plurality of electronic circuits.

For example, circuitry 152 may serve as elements among the elements ofencoder 100 illustrated in FIG. 1 other than the elements for storinginformation. Namely, circuitry 150 may perform the above-describedoperations as the operations of these elements.

Memory 152 is a dedicated or general-purpose memory that storesinformation for circuitry 152 to encode videos. Memory 152 may be anelectronic circuit and connected to circuitry 150 or included incircuitry 160.

Memory 152 may be an aggregate of a plurality of electronic circuits ormay include a plurality of sub memories. Memory 152 may be a magneticdisk or an optical disc, and may be expressed as storage or recordingmedium. Memory 162 may be nonvolatile memory or volatile memory.

For example, memory 152 may serve as elements for storing information,among the elements of encoder 100 illustrated in FIG. 1 .

Memory 152 may store an encoded video or a bit string corresponding tothe encoded video. Memory 152 may also store a program for circuitry 150to encode a video.

Note that encoder 100 may not include all the elements illustrated inFIG. 1 , and may not perform all the processes described above. One ormore of the elements illustrated in FIG. 1 may be included in anotherdevice, or one or more of the processes described above may be performedby another device. One or more of the elements illustrated in FIG. 1 areimplemented by encoder 100, and with one or more of the above-describedprocesses carried out, information related to the encoding of the videois appropriately set.

FIG. 34 is a flowchart illustrating an example of an operation performedby encoder 100. For example, encoder 100 illustrated in FIG. 33 performsthe operation illustrated in FIG. 34 when splitter 102 splits a currentchroma block. Specifically, circuitry 150 performs the followingoperation using memory 152.

First, encoder 100 determines whether the shape of a current chromablock to be split satisfies a first condition (S16001).

When the shape of the current chroma block satisfies the first condition(Yes in S16001), encoder 100 generates second candidates including aplurality of block partitioning method candidates by eliminating one ormore predetermined block partitioning method candidates from firstcandidates including a plurality of block partitioning methods (S16002).

Note that the candidate eliminated at S16002 may include a candidatethat splits a block having one side longer than the other side so that aratio of one side to the other side further increases. In addition, thecandidate eliminated at S16002 may include a candidate that splits intotwo a block having one side longer than the other side so that a ratioof one side to the other side further increases. Moreover, the candidateeliminated at S16002 may include a candidate that splits into three ablock having one side longer than the other side so that a ratio of oneside to the other side further increases.

Encoder selects a block partitioning method candidate from among thesecond candidates for a block partitioning method (S16003).

Subsequently, encoder 100 splits the current chroma block according tothe block partitioning method selected at step S16003 (S16005). Encoder100 then ends the operation.

When the shape of the current chroma block does not satisfy the firstcondition (No in S16001), on the other hand, encoder 100 selects a blockpartitioning method candidate from among the first candidates includinga plurality of candidates for a block partitioning method (S16004).

Subsequently, encoder 100 splits the current chroma block according tothe block partitioning method selected at step S16004 (S16005). Encoder100 then ends the operation.

FIG. 35 is a block diagram illustrating an example of implementation ofdecoder 200. Decoder 200 includes processing circuitry 250 and memory252. For example, the elements of decoder 200 illustrated in FIG. 10 areimplemented by processing circuitry 250 and memory 252 illustrated inFIG. 35 .

Circuitry 250 is an electronic circuit accessible to memory 252 andprocesses information. For example, circuitry 260 is a dedicated orgeneral-purpose electronic circuit which decodes videos using memory252. Circuitry 250 may be a processor such as a CPU. Circuitry 250 maybe an aggregate of a plurality of electronic circuits.

For example, circuitry 250 may serve as at least two of the elements ofdecoder 200 illustrated in FIG. 10 , other than the elements for storinginformation. Namely, circuitry 250 may perform the above-describedoperations as the operations of these elements.

Memory 252 is a dedicated or general-purpose memory that storesinformation for circuitry 250 to encode videos. Memory 252 may be anelectronic circuit and connected to circuitry 250.

Memory 252 may be an aggregate of a plurality of electronic circuits ormay include a plurality of sub memories. Memory 252 may be a magneticdisk or an optical disc, and may be expressed as storage or recordingmedium. Memory 252 may be nonvolatile memory or volatile memory.

For example, memory 252 may serve as elements for storing information,among the elements of decoder 200 illustrated in FIG. 35 .

Memory 252 may store a decoded video and a bit string corresponding tothe decoded video. Memory 252 may also store a program for circuitry 250to decode videos.

Note that decoder 200 may not include all the elements illustrated inFIG. 10 , and may not perform all the processes described above. One ormore of the elements illustrated in FIG. 10 may be included in anotherdevice, and one or more of the processes described above may beperformed by another device. One or more of the elements illustrated inFIG. 10 are implemented by decoder 200, and with one or more of theabove-described processes carried out, information relating to thedecoding of the video is appropriately set.

FIG. 36 is a flowchart illustrating an example of an operation performedby decoder 200. For example, decoder 200 illustrated in FIG. 35 performsthe operation illustrated in FIG. 36 when splitting a current chromablock. Specifically, circuitry 250 performs the following operationusing memory 252.

First, decoder 200 generates second candidates including a plurality ofblock partitioning method candidates by eliminating one or morepredetermined block partitioning method candidates from first candidatesincluding a plurality of block partitioning method candidates (S17001).

Decoder 200 selects a block partitioning method candidate from among thesecond block coding method candidates (S17002).

Subsequently, decoder 200 splits the current chroma block according tothe block partitioning method selected in step S17002 (S17003). Decoder200 then ends the operation.

[Supplemental Information]

Encoder 100 and decoder 200 according to the present embodiment may beused as an image encoder and an image decoder, respectively, or may beused as a video encoder and a video decoder, respectively.

In the present embodiment, each of the elements may be configured ofdedicated hardware or may be implemented by executing a software programsuitable for the element. Each of the elements may be implemented by aprogram executor such as a CPU or a processor reading and executing asoftware program recorded on a recording medium such as a hard disc or asemiconductor memory.

Specifically, encoder 100 and decoder 200 may each include processingcircuitry, and storage electrically coupled to the processing circuitryand accessible from the processing circuitry. For example, theprocessing circuitry corresponds to processor 150 or 250 and the storagecorresponds to memory 152 or 252.

The processing circuitry includes at least one of the dedicated hardwareand the program executor, and performs processing using the storage. Ifthe processing circuitry includes a program executor, the storage storesa software program to be executed by the program executor.

Here, the software which implements encoder 100 or decoder 200 accordingto the present embodiment, for instance, is a program as follows.

Namely, the program causes a computer to execute: determining whether ashape of a current block to be split in an image satisfies a firstcondition; generating one or more second candidates for a blockpartitioning method by eliminating one or more predetermined candidatesfrom a plurality of first candidates for a block partitioning methodwhen the shape of the current block satisfies the first condition;selecting a block partitioning method from among the one or more secondcandidates; and splitting the current block according to the blockpartitioning method selected.

Alternatively, the program may cause the computer to parse, from abitstream generated by encoding the image, block partitioninginformation relating to a block partitioning method according to which acurrent block in an image is split, and split the current block based onthe block partitioning information that has been parsed. When thecurrent block in the image satisfies a first condition, the blockpartitioning information may be generated by generating one or moresecond candidates for a block partitioning method and selecting a blockpartitioning method from among the second candidates generated byeliminating one or more predetermined candidates from first candidates.

The elements may be circuits as described above. These circuits mayconstitute one circuitry as a whole, or may be separate circuits. Eachelement may be implemented by a general-purpose processor or by adedicated processor.

Processing performed by a specific element may be performed by adifferent element. The order of performing processes may be changed orthe processes may be performed in parallel. An encoder/decoder mayinclude encoder 100 and decoder 200.

The ordinal numbers such as the first and the second used in thedescription may be switched where necessary. A new ordinal number may beprovided for or any of the existing ordinal numbers may be removed fromthe elements.

The above has given a description of aspects of encoder 100 and decoder200 based on the embodiments, yet the aspects of encoder 100 and decoder200 are not limited to the embodiments. The aspects of encoder 100 anddecoder 200 may also encompass various modifications that may beconceived by those skilled in the art to the embodiments, andembodiments achieved by combining elements in different embodiments,without departing from the scope of the present disclosure.

This aspect may be implemented in combination with at least one or moreof the other aspects according to the present disclosure.

Embodiment 2

As described in each of the above embodiments, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoder/decoder that includes both the image encoder and the imagedecoder. Other configurations included in the system may be modified ona case-by-case basis.

USAGE EXAMPLES

FIG. 37 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 38 , which is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 38 . Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 39 , metadata is storedusing a data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 40 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 41 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 40 and FIG. 41 , a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

OTHER USAGE EXAMPLES

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 42 illustrates smartphone ex115. FIG. 43 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, one ormore of the processes in the flowcharts, one or more of the constituentelements of the apparatuses, and part of the syntax described in thisaspect may be implemented in combination with other aspects.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, digital camcorders, video conference systems,and electron mirrors.

1-10. (canceled)
 11. An encoder, comprising: circuitry; and memorycoupled to the circuitry, wherein the circuitry, in operation:determines whether a shape of a current chroma block to be split in animage satisfies a first condition; generates one or more secondcandidates for a block partitioning method by eliminating one or morepredetermined candidates from a plurality of first candidates for ablock partitioning method when the shape of the current chroma blocksatisfies the first condition; selects a block partitioning method fromamong the one or more second candidates; and splits the current chromablock according to the block partitioning method selected, and theplurality of first candidates include at least a ternary splitting invertical direction and the one or more second candidates exclude theternary splitting in vertical direction.
 12. A decoder, comprising:circuitry; and memory coupled to the circuitry, wherein the circuitry,in operation: parses, from an encoded bitstream generated by encoding animage, block partitioning information relating to a block partitioningmethod according to which a current chroma block to be split in theimage is split; and splits the current chroma block based on the blockpartitioning information parsed, when a shape of the current chromablock satisfies a first condition, the block partitioning information isgenerated by (i) generating one or more second candidates for a blockpartitioning method by eliminating one or more predetermined candidatesfrom a plurality of first candidates for a block partitioning method and(ii) selecting a block partitioning method from among the one or moresecond candidates, and the plurality of first candidates include atleast a ternary splitting in vertical direction and the one or moresecond candidates exclude the ternary splitting in vertical direction.